1. Field of the Invention
The present invention relates to a projection-type image display apparatus including a light source unit and an optical modulator configured to modulate a light beam emitted from the light source unit.
2. Description of the Related Art
Conventionally, there has been widely known a projection-type image display apparatus (a liquid crystal projector, for example) including: a light source configured to emit a rectangular or circular light beam; an optical modulator (hereinafter, referred to as a “liquid crystal panel”) configured to modulate the light beam emitted from the light source; and a projection lens configured to enlarge the light beam outputted from the liquid crystal panel and then to project the light beam on a screen.
In general, in a light beam emitted from a light source, the center portion of the light beam is brighter than that of the portion surrounding the center portion. For this reason, when a liquid crystal panel is directly radiated with the light beam from the light source, the illuminance distribution of the light beam radiated on the liquid crystal panel becomes uneven. In other words, the illuminance distribution of the light beam radiated on the screen becomes uneven.
For this reason, the aforementioned projection-type image display apparatus includes a pair of fly-eye lenses each having micro lenses arranged in an array, and a condenser lens configured to condense, on the entire liquid crystal panel, the light beams collected by the micro lenses.
Thus, the condenser lens causes the light beams collected by the micro lenses to overlap with one another on the entire liquid crystal panel. This results in obtaining evenness in the illuminance distribution of the light on the screen, and the minimized color irregularities of video displayed on the screen (refer to Optical Society of Japan, Japan Kogaku (Japanese Journal of Optics) “Kogaku-Ekisho projector no Kougakukei (Optics System of Liquid Crystal Projector)” vol. 32 (2002) (hereinafter, referred to as “Non-patent Document 1”).
In general, a liquid crystal panel includes a pair of polarizers (an incident side polarizer and an output side polarizer) to obtain black and white contrast. Specifically, each of the polarizers has a characteristic of allowing a light beam in a first polarization direction to pass through while not allowing a light beam in a second direction orthogonal to the first direction to pass through. Furthermore, the first polarization direction of a light beam allowed to pass through a first polarizer (hereinafter, referred to as a “light transmitting polarization direction” or a “transmission axis”) is orthogonal to the second polarization direction of a light beam allowed to pass through a second polarizer (hereinafter, referred to as a “light transmitting polarization direction” or a “transmission axis”). Specifically, the polarizing direction of a light beam not allowed to pass through the first polarizer (hereinafter, referred to as a “light absorbing polarization direction” or an “absorb axis”) is orthogonal to the polarizing direction of a light beam not allowed to pass through the second polarizer (hereinafter, referred to as a “light absorbing polarization direction” or an “absorb axis”).
Incidentally, when natural light (random polarization) enters the incident side polarizer of a liquid crystal panel, half of the light is lost (in theory). For this reason, there has been known a liquid crystal display device, provided with polarization conversion means having a PBS array or the like, disposed between the incident side polarizer and the light source. In this liquid crystal display apparatus, the polarization conversion means causes natural light to enter the polarizer, after changing the polarization direction of the natural light to match with the light transmitting polarization direction of the polarizer on the incident light side, to improve the light utilization efficiency (Japanese Patent Publication No. 2000-180794, for example).
However, although the directions of light beams entering the incident side polarizer are aligned with one another by the aforementioned polarization conversion means, the light beams entering the incident side polarizer include a light entering the incident side polarizer from an oblique direction, such as a light beam not in parallel with the optical axis. The presence of such a light beam results in reduction of black and white contrast.
Specifically, consider a case where an angle formed by the absorb axis of the incident polarizer and the projection vector on the incident side polarizer of a light beam entering the incident side polarizer is large, and where an angle formed by the projection vector and the transmission axis of the incident polarizer (that is, the absorb axis of the output polarizer) is also large. In this case, the transmissivity of a light beam passing through the aforementioned pair of polarizers increases since sufficient extinction under crossed Nicols cannot be obtained. Moreover, in a case where an angle (an incident angle) formed by a light beam entering the incident side polarizer and the optical axis (a line perpendicular to the incident surface of the incident side polarizer) is large, black and white contrast is reduced since the transmissivity of a light beam passing through the pair of the polarizers increases.
In addition, as disclosed in Non-patent Document 1, in a case where an optical system using fly-eye lenses is employed, light beams from various directions enter the incident surface of the incident side polarizer. This is because each of the fly-eye lenses is provided so as to cause the light beams collected by the micro lenses of the fly-eye lens to overlap with one another, on the entire liquid crystal panel. Accordingly, light beams enter the incident surface of the polarizer from various directions. This makes prominent the reduction in contrast caused by an increase in the transmissivity of the light beam passing through the pair of polarizers.